Variable role of the long terminal repeat Sp1-binding sites in human immunodeficiency virus replication in T lymphocytes

The HIV-Tat protein interacts with Sp3 transcription factor and inhibits its binding to a distal site of the sod2 promoter in human pulmonary artery endothelial cells

Redox imbalance results in damage to cellular macromolecules and interferes with signaling pathways, leading to an inflammatory cellular and tissue environment. As such, the cellular oxidative environment is tightly regulated by several redox-modulating pathways. Many viruses have evolved intricate mechanisms to manipulate these pathways for their benefit, including HIV-1, which requires a pro-oxidant cellular environment for optimal replication. One such virulence factor responsible for modulating the redox environment is the HIV Transactivator of transcription (Tat). Tat is of particular interest as it is actively secreted by infected cells and internalized by uninfected bystander cells where it can elicit pro-oxidant effects resulting in inflammation and damage. Previously, we demonstrated that Tat regulates basal expression of Superoxide Dismutase 2 (sod2) by altering the binding of the Sp-transcription factors at regions relatively near (approx. -210 nucleotides) upstream of the transcriptional start site. Now, using in silico analysis and a series of sod2 promoter reporter constructs, we have identified putative clusters of Sp-binding sites located further upstream of the proximal sod2 promoter, between nucleotides -3400 to -210, and tested their effect on basal transcription and for their sensitivity to HIV-1 Tat. In this report, we demonstrate that under basal conditions, maximal transcription requires a cluster of Sp-binding sites in the -584 nucleotide region, which is extremely sensitive to Tat. Using chromatin immunoprecipitation (ChIP) we demonstrate that Tat results in altered occupancy of Sp1 and Sp3 at this distal Tat-sensitive regulatory element and strongly stimulated endogenous expression of SOD2 in human pulmonary artery endothelial cells (HPAEC). We also report altered expression of Sp1 and Sp3 in Tat-expressing HPAEC as well as in the lungs of HIV-1 infected humanized mice. Lastly, Tat co-immunoprecipitated with endogenous Sp3 but not Sp1 and did not alter the acetylation state of Sp3. Thus, here, we have defined a novel and important cis-acting factor in HIV-1 Tat-mediated regulation of SOD2, demonstrated that modulation of Sp1 and Sp3 activity by Tat promotes SOD2 expression in primary human pulmonary artery endothelial cells and determined that pulmonary levels of Sp3 as well as SOD2 are increased in the lungs of a mouse model of HIV infection.

Expression of an RNA glycosidase inhibits HIV-1 transactivation of transcription

HIV-1 (human immunodeficiency virus) transcription is primarily controlled by the virally encoded Tat (transactivator of transcription) protein and its interaction with the viral TAR (transcription response element) RNA element. Specifically, binding of a Tat-containing complex to TAR recruits cellular factors that promote elongation of the host RNA polymerase engaging the viral DNA template. Disruption of this interaction halts viral RNA transcription. In the present study, we investigated the effect of pokeweed antiviral protein (PAP), an RNA glycosidase (EC#: 3.2.2.22) synthesized by the pokeweed plant (Phytolacca americana), on transcription of HIV-1 mRNA. We show that co-expression of PAP with a proviral clone in culture cells resulted in a Tat-dependent decrease in viral mRNA levels. PAP reduced HIV-1 transcriptional activity by inhibiting Tat protein synthesis. The effects of PAP expression on host factors AP-1 (activator protein 1), NF-κB (nuclear factor kappa-light-chain-enhancer of activated B-cells) and specificity protein 1, which modulate HIV-1 transcription by binding to the viral LTR (5'-long terminal repeat), were also investigated. Only AP-1 showed a modest JNK pathway-dependent increase in activity in the presence of PAP; however, this activation was not sufficient to significantly enhance transcription from a partial viral LTR containing AP-1 binding sites. Therefore, the primary effect of PAP on HIV-1 transcription is to reduce viral RNA synthesis by decreasing the abundance of Tat. These findings provide a mechanistic explanation for the observed decrease in viral RNAs in cells expressing PAP and contribute to our understanding of the antiviral effects of this plant protein.

Functional properties of the HIV-1 long terminal repeat containing single-nucleotide polymorphisms in Sp site III and CCAAT/enhancer binding protein site I

BACKGROUND

HIV-1 gene expression is driven by the long terminal repeat (LTR), which contains many binding sites shown to interact with an array of host and viral factors. Selective pressures within the host as well as the low fidelity of reverse transcriptase lead to changes in the relative prevalence of genetic variants within the HIV-1 genome, including the LTR, resulting in viral quasispecies that can be differentially regulated and can potentially establish niches within specific cell types and tissues.

METHODS

Utilizing flow cytometry and electromobility shift assays, specific single-nucleotide sequence polymorphisms (SNPs) were shown to alter both the phenotype of LTR-driven transcription and reactivation. Additional studies also demonstrated differential loading of transcription factors to probes derived from the double-variant LTR as compared to probes from the wild type.

RESULTS

This study has identified specific SNPs within CCAAT/enhancer binding protein (C/EBP) site I and Sp site III (3 T, C-to-T change at position 3, and 5 T, C-to-T change at position 5 of the binding site, respectively) that alter LTR-driven gene transcription and may alter the course of viral latency and reactivation. The HIV-1 LAI LTRs containing the SNPs of interest were coupled to a plasmid encoding green fluorescent protein (GFP), and polyclonal HIV-1 LTR-GFP stable cell lines utilizing bone marrow progenitor, T, and monocytic cell lines were constructed and utilized to explore the LTR phenotype associated with these genotypic changes.

CONCLUSIONS

Although the 3 T and 5 T SNPs have been shown to be low-affinity binding sites, the fact that they can still result in effective HIV-1 LTR-driven gene expression, particularly within the TF-1 cell line, has suggested that the low binding site affinities associated with the 3 T C/EBP site I and 5 T Sp site III are potentially compensated for by the interaction of nuclear factor-κB with its corresponding binding sites under selected physiological and cellular conditions. Additionally, tumor necrosis factor-α and Tat can enhance basal transcription of each SNP-specific HIV-1 LTR; however, differential regulation of the LTR is both SNP- and cell type-specific.

Marine teleost ortholog of catalase from rock bream (Oplegnathus fasciatus): molecular perspectives from genomic organization to enzymatic behavior with respect to its potent antioxidant properties

Catalases are well known antioxidant enzymes that can mainly dismutate hydrogen peroxide into water and oxygen in order to prevent oxidative stress. The complete genomic DNA (gDNA) sequence of the catalase gene from rock bream (Oplegnathus fasciatus) was identified from our custom-constructed BAC genomic DNA library and designated as RbCat. RbCat consists of 13 exons, separated by 12 introns, within a 13,722-bp gDNA sequence. The complete cDNA sequence (3303 bp) of RbCat is comprised of a 1581-bp coding region, encoding a peptide of 527 amino acids (aa) in length, with a predicted molecular mass of 60 kDa and a theoretical isoelectric point of 8.34. The anticipated promoter region of RbCat contains several transcription factor-binding sites, including sites that bind with immune- and antioxidant-responsive signaling molecules, suggesting its substantial transcriptional regulation. RbCat resembles the typical catalase family signature, i.e., it is composed of the catalase proximal active site motif along with a catalase proximal heme-ligand signature motif and shares great homology with its fish counterparts. According to multiple sequence alignment, functionally important amino acids present in RbCat were thoroughly conserved among its vertebrate counterparts. Phylogenetic analysis revealed that RbCat evolved from a vertebrate origin, and further positioned it in the fish clade. Recombinant RbCat had noticeable peroxidase activity against its substrate, hydrogen peroxide, in a dose-dependent manner. However, it demonstrated substantial peroxidase activity within a broad range of temperatures and pH values. Constitutive RbCat mRNA expression of different magnitudes was detected in a tissue-specific manner, suggesting its diverse role in physiology with respect to the tissue type. Moreover, immune challenge experiments using Edwardsiella tarda and rock bream iridovirus (RBIV) as live pathogens and polyinosinic:polycytidylic acid and lipopolysaccharide as mitogens revealed that the transcription of RbCat can be modulated by immune stimulation. Collectively, the results obtained in this study suggest that RbCat can function as a potent antioxidant enzyme in rock bream and may play a role in post-immune responses with respect to its peroxidase activity.

Multiple NF-κB sites in HIV-1 subtype C long terminal repeat confer superior magnitude of transcription and thereby the enhanced viral predominance

We demonstrate that at least three different promoter variant strains of HIV-1 subtype C have been gradually expanding and replacing the standard subtype C viruses in India, and possibly in South Africa and other global regions, over the past decade. The new viral strains contain an additional NF-κB, NF-κB-like, or RBEIII site in the viral promoter. Although the acquisition of an additional RBEIII site is a property shared by all the HIV-1 subtypes, acquiring an additional NF-κB site remains an exclusive property of subtype C. The acquired κB site is genetically distinct, binds the p50-p65 heterodimer, and strengthens the viral promoter at the levels of transcription initiation and elongation. The 4-κB viruses dominate the 3-κB "isogenic" viral strains in pairwise competition assays in T-cell lines, primary cells, and the ecotropic human immunodeficiency virus mouse model. The dominance of the 4-κB viral strains is also evident in the natural context when the subjects are coinfected with κB-variant viral strains. The mean plasma viral loads, but not CD4 counts, are significantly different in 4-κB infection suggesting that these newly emerging strains are probably more infectious. It is possible that higher plasma viral loads underlie selective transmission of the 4-κB viral strains. Several publications previously reported duplication or deletion of diverse transcription factor-binding sites in the viral promoter. Unlike previous reports, our study provides experimental evidence that the new viral strains gained a potential selective advantage as a consequence of the acquired transcription factor-binding sites and importantly that these strains have been expanding at the population level.

Regulation of Mycobacterium tuberculosis-dependent HIV-1 transcription reveals a new role for NFAT5 in the toll-like receptor pathway

Tuberculosis (TB) disease in HIV co-infected patients contributes to increased mortality by activating innate and adaptive immune signaling cascades that stimulate HIV-1 replication, leading to an increase in viral load. Here, we demonstrate that silencing of the expression of the transcription factor nuclear factor of activated T cells 5 (NFAT5) by RNA interference (RNAi) inhibits Mycobacterium tuberculosis (MTb)-stimulated HIV-1 replication in co-infected macrophages. We show that NFAT5 gene and protein expression are strongly induced by MTb, which is a Toll-like receptor (TLR) ligand, and that an intact NFAT5 binding site in the viral promoter of R5-tropic HIV-1 subtype B and subtype C molecular clones is required for efficent induction of HIV-1 replication by MTb. Furthermore, silencing by RNAi of key components of the TLR pathway in human monocytes, including the downstream signaling molecules MyD88, IRAK1, and TRAF6, significantly inhibits MTb-induced NFAT5 gene expression. Thus, the innate immune response to MTb infection induces NFAT5 gene and protein expression, and NFAT5 plays a crucial role in MTb regulation of HIV-1 replication via a direct interaction with the viral promoter. These findings also demonstrate a general role for NFAT5 in TLR- and MTb-mediated control of gene expression.

The major cause of AIDS deaths globally has been tuberculosis (TB), which is caused by the bacterium Mycobacterium tuberculosis (MTb). Co-infection with MTb exacerbates human immunodeficiency virus type1 (HIV-1) replication and disease progression via both innate and adaptive host immune responses to MTb infection. In this report, we present evidence that the transcription factor NFAT5 plays a crucial role in MTb-induced HIV-1 replication in human peripheral blood cells and monocytes. We also show that MTb infection itself stimulates NFAT5 gene expression in human monocytes and that its expression involves the TLR signalling pathway and requires the downstream adaptor proteins MyD88, IRAK1, and TRAF6. This identification of a novel role for NFAT5 in TB/HIV-1 co-infection reveals that NFAT5 is a major mediator of TLR-dependent gene expression and thus provides a potential new therapeutic target for treatment of HIV-1 and possibly other diseases.

Insights into cellular factors that regulate HIV-1 replication in human cells

Retroviruses integrate into the host cell's chromosome. Accordingly, many aspects of the life cycle of retroviruses like HIV-1 are intimately linked to the functions of cellular proteins and RNAs. In this review, we discuss in brief recent genomewide screens for the identification of cellular proteins that assist HIV-1 replication in human cells. We also review findings for other cellular moieties that help or restrict the viral life cycle.

Regulation of HIV-1 transcription in cells of the monocyte-macrophage lineage

Human immunodeficiency virus type 1 (HIV-1) has been shown to replicate productively in cells of the monocyte-macrophage lineage, although replication occurs to a lesser extent than in infected T cells. As cells of the monocyte-macrophage lineage become differentiated and activated and subsequently travel to a variety of end organs, they become a source of infectious virus and secreted viral proteins and cellular products that likely initiate pathological consequences in a number of organ systems. During this process, alterations in a number of signaling pathways, including the level and functional properties of many cellular transcription factors, alter the course of HIV-1 long terminal repeat (LTR)-directed gene expression. This process ultimately results in events that contribute to the pathogenesis of HIV-1 infection. First, increased transcription leads to the upregulation of infectious virus production, and the increased production of viral proteins (gp120, Tat, Nef, and Vpr), which have additional activities as extracellular proteins. Increased viral production and the presence of toxic proteins lead to enhanced deregulation of cellular functions increasing the production of toxic cellular proteins and metabolites and the resulting organ-specific pathologic consequences such as neuroAIDS. This article reviews the structural and functional features of the cis-acting elements upstream and downstream of the transcriptional start site in the retroviral LTR. It also includes a discussion of the regulation of the retroviral LTR in the monocyte-macrophage lineage during virus infection of the bone marrow, the peripheral blood, the lymphoid tissues, and end organs such as the brain. The impact of genetic variation on LTR-directed transcription during the course of retrovirus disease is also reviewed.

O-linked N-acetylglucosaminylation of Sp1 inhibits the human immunodeficiency virus type 1 promoter

Human immunodeficiency virus type 1 (HIV-1) gene expression and replication are regulated by the promoter/enhancer located in the U3 region of the proviral 5' long terminal repeat (LTR). The binding of cellular transcription factors to specific regulatory sites in the 5' LTR is a key event in the replication cycle of HIV-1. Since transcriptional activity is regulated by the posttranslational modification of transcription factors with the monosaccharide O-linked N-acetyl-D-glucosamine (O-GlcNAc), we evaluated whether increased O-GlcNAcylation affects HIV-1 transcription. In the present study we demonstrate that treatment of HIV-1-infected lymphocytes with the O-GlcNAcylation-enhancing agent glucosamine (GlcN) repressed viral transcription in a dose-dependent manner. Overexpression of O-GlcNAc transferase (OGT), the sole known enzyme catalyzing the addition of O-GlcNAc to proteins, specifically inhibited the activity of the HIV-1 LTR promoter in different T-cell lines and in primary CD4(+) T lymphocytes. Inhibition of HIV-1 LTR activity in infected T cells was most efficient (>95%) when OGT was recombinantly overexpressed prior to infection. O-GlcNAcylation of the transcription factor Sp1 and the presence of Sp1-binding sites in the LTR were found to be crucial for this inhibitory effect. From this study, we conclude that O-GlcNAcylation of Sp1 inhibits the activity of the HIV-1 LTR promoter. Modulation of Sp1 O-GlcNAcylation may play a role in the regulation of HIV-1 latency and activation and links viral replication to the glucose metabolism of the host cell. Hence, the establishment of a metabolic treatment might supplement the repertoire of antiretroviral therapies against AIDS.

Derivation of infectious HIV-1 molecular clones with LTR mutations: sensitivity to the CD8+ cell noncytotoxic anti-HIV response

CD8(+) cells from healthy, asymptomatic HIV-1-infected individuals can inhibit HIV-1 replication in naturally or acutely infected CD4(+) cells in the absence of cell killing. This CD8(+) cell noncytotoxic anti-HIV response (CNAR) is mediated by a soluble CD8(+) cell antiviral factor (CAF). CNAR/CAF inhibits HIV-1 replication by blocking viral RNA transcription. HIV transcription is regulated by a variety of cis-acting DNA sequence elements within the proviral long terminal repeat (LTR). We hypothesized that one of the HIV-1 LTR proviral DNA sequence elements that binds host cell transcriptional factors is involved in this antiviral activity. To assess this possibility, we constructed full-length infectious HIV-1 molecular clones with mutations in the LTR elements NFAT, AP-1, IL-2 homology region, and the downstream ISRE. We also tested full-length infectious molecular clones that had deletions of either the NF-kappaB or Sp1 sites of the LTR or lacked functional Tat and TAR elements. Viruses generated from these molecular clones were used to acutely infect CD4(+) cells that subsequently were either co-cultured with CD8(+) cells from individuals that exhibited strong CNAR or cultured with CAF-containing fluids. The replication of all of the mutant HIV-1 viruses tested was substantially reduced in the presence of CNAR/CAF. These findings suggest that other regions in the viral LTR or other host cell processes are involved in the transcriptional block elicited by CNAR/CAF.

c-Myc and Sp1 contribute to proviral latency by recruiting histone deacetylase 1 to the human immunodeficiency virus type 1 promoter

Histone deacetylase (HDAC) inhibitors such as valproic acid (VPA) induce the expression of quiescent proviral human immunodeficiency virus type 1 (HIV-1) and may deplete proviral infection in vivo. To uncover novel molecular mechanisms that maintain HIV latency, we sought cellular mRNAs whose expression was diminished in resting CD4(+) T cells of HIV-1-infected patients exposed to VPA. c-Myc was prominent among genes markedly downregulated upon exposure to VPA. c-Myc expression repressed HIV-1 expression in chronically infected cell lines. Chromatin immunoprecipitation (ChIP) assays revealed that c-Myc and HDAC1 are coordinately resident at the HIV-1 long terminal repeat (LTR) promoter and absent from the promoter after VPA treatment in concert with histone acetylation, RNA polymerase II recruitment, and LTR expression. Sequential ChIP assays demonstrated that c-Myc, Sp1, and HDAC1 coexist in the same DNA-protein complex at the HIV promoter. Short hairpin RNA inhibition of c-Myc reduces both c-Myc and HDAC1 occupancy, blocks c-Myc repression of Tat activation, and increases LTR expression. These results expand the understanding of mechanisms that recruit HDAC and maintain the latency of HIV-1, suggesting novel therapeutic approaches against latent proviral HIV infection.

The Werner Syndrome Helicase Is a Cofactor for HIV-1 Long Terminal Repeat Transactivation and Retroviral Replication

The Werner syndrome helicase (WRN) participates in DNA replication, double strand break repair, telomere maintenance, and p53 activation. Mutations of wrn cause Werner syndrome (WS), an autosomal recessive premature aging disorder associated with cancer predisposition, atherosclerosis, and other aging related symptoms. Here, we report that WRN is a novel cofactor for HIV-1 replication. Immortalized human WRN(-/-) WS fibroblasts, lacking a functional wrn gene, are impaired for basal and Tat-activated HIV-1 transcription. Overexpression of wild-type WRN transactivates the HIV-1 long terminal repeat (LTR) in the absence of Tat, and WRN cooperates with Tat to promote high-level LTR transactivation. Ectopic WRN induces HIV-1 p24(Gag) production and retroviral replication in HIV-1-infected H9(HIV-1IIIB) lymphocytes. A dominant-negative helicase-minus mutant, WRN(K577M), inhibits LTR transactivation and HIV-1 replication. Inhibition of endogenous WRN, through co-expression of WRN(K577M), diminishes recruitment of p300/CREB-binding protein-associated factor (PCAF) and positive transcription elongation factor b (P-TEFb) to Tat/transactivation response-RNA complexes, and immortalized WRN(-/-) WS fibroblasts exhibit comparable defects in recruitment of PCAF and P-TEFb to the HIV-1 LTR. Our results demonstrate that WRN is a novel cellular cofactor for HIV-1 replication and suggest that the WRN helicase participates in the recruitment of PCAF/P-TEFb-containing transcription complexes. WRN may be a plausible target for antiretroviral therapy.

Cooperativity between Rad51 and C/EBP family transcription factors modulates basal and Tat-induced activation of the HIV-1 LTR in astrocytes

Transcription of the HIV-1 genome is a complex event that requires functional and physical communication of cellular proteins that recognize the LTR sequence with viral proteins, most notably, Tat. Moreover, studies have revealed the ability of Tat to induce transcription of a variety of cellular genes whose products can affect the status of cells, thus contributing to the pathogenesis of AIDS. Recently, we demonstrated that expression of Tat in astrocytes and other neural cells leads to upregulation of Rad51, a major component of DNA repair via homologous recombination. The unscheduled upregulation of Rad51, in turn, has an impact upon the extent of chromosomal abnormalities that are seen in Tat-producing cells. Here, we asked whether an elevation in Rad51 levels influences the extent of viral gene transcription in astrocytic cells. Our results demonstrate that ectopic expression of Rad51 enhances the basal- and the Tat-induced transcription of the LTR promoter. This event requires cooperativity from the C/EBP family of transcription factors including C/EBPbeta and C/EBPbeta homologous protein (CHOP). Similar to Tat, we showed that Rad51 interacts with C/EBPbeta and augments its interaction with the DNA motif spanning nucleotides -120 to -94 of the LTR. Interestingly, Tat exhibited the capacity to augment the synergism between Rad51 and C/EBPbeta. Our results also demonstrate that the level of activation of the LTR by CHOP and Tat, either alone or together, is elevated in the presence of the SW1/SNF1 chromatin remodeling complex. These observations unravel a new pathway for Tat activation of the LTR that includes the positive feedback loop involving Rad51 and C/EBPbeta family proteins.

2-Deoxyglucose: An anticancer and antiviral therapeutic, but not any more a low glucose mimetic

2-Deoxyglucose (2-DG), a non-metabolizable glucose analogue, blocks glycolysis and inhibits protein glycosylation. It has been tested in multiple studies for possible application as an anticancer or antiviral therapeutic. The inhibitory effect of 2-DG on ATP generation made it a good candidate molecule as a calorie restriction mimetic as well. Furthermore, 2-DG has been utilized in numerous studies to simulate a condition of glucose starvation. Because 2-DG disrupts glucose metabolism, protein glycosylation, and ER quality control at the same time, a cellular or pathologic outcome could be easily misinterpreted without clear understanding of 2-DG's effect on each of these aspects. However, the effect of 2-DG on protein glycosylation has rarely been investigated. A recent study suggested that 2-DG causes hyperGlcNAcylation of proteins, while low glucose supply causes hypoGlcNAcylation. In certain aspects of cellular physiology, this difference could be disregarded, but in others, this may possibly cause totally different outcomes.

Conditional expression of IFN-alpha and IFN-gamma activated by HBV as genetic therapy for hepatitis B

Chronic infection with hepatitis B virus (HBV) has potentially devastating consequences and is very difficult to treat. Therapy with recombinant interferons (IFN), especially IFN-alpha, may be effective. The blood IFN-alpha levels that are needed to maintain therapeutic IFN-alpha levels in the liver, however, often cause severe side effects. Gene delivery to the liver may provide a solution. Using a long-term expression construct could provide the desired levels of IFN locally without the need to maintain potentially problematic blood levels. Recombinant, Tag-deleted SV40-derived vectors transduce hepatocytes efficiently and provide permanent transgene expression. We designed an expression construct that was effective against HBV and whose activity was limited to HBV-infected cells. To do this, we exploited the ability of HBV X protein to activate NF-kappaB and, via NF-kappaB, to activate promoter activity of HIV long terminal repeat (LTR) in hepatocytes. Using HIVLTR as a conditional promoter upstream of human and murine IFN-alpha and IFN-gamma cDNAs, rSV40 vectors were used to test the responsiveness of IFN to HBV and the ability of these IFNs to inhibit HBV transcripts and protein production and to activate IFN signaling in neighboring untransduced cells. We found that in hepatocyte cell lines and in primary hepatocytes, HBV activated the promoter activity of the HIVLTR via NF-kappaB. When whole HBV genome was delivered to cells by transfection to simulate HBV infection, IFN expression was activated, IFNs were produced and secreted, and they protected cells from HBV. Levels of IFN proteins that were secreted in this context were comparable to targeted blood levels needed to control chronic hepatitis viral infection. Further, IFNs that were elicited and secreted in this manner were able to activate IFN-induced signaling pathways in neighboring, untransduced cells and so were likely to provide protection even to cells that the rSV40 vector did not transduce. Gene delivery using such rSV40 vectors expressing IFNs conditionally in response to HBV may be an attractive therapeutic option for the treatment of chronic hepatitis B.

Differential regulation of human immunodeficiency virus type 2 and simian immunodeficiency virus promoter activity

Promoter activity of the HIV-1 long terminal repeat (LTR) is largely dependent on intact NF-kB and SpI binding sites in the U3 region. In contrast, upstream LTR sequences allow efficient simian immunodeficiency virus (SIVmac) transcription in the absence of the core enhancer promoter region. In the present study, we investigated whether the regulation of HIV-2 Rod LTR activity is more reminiscent of HIV-1 having the same host or of SIVmac239 belonging to the same phylogenetic group. Viral promoter activity was studied in the context of the integrated provirus using both single cycle assays with pseudotyped luciferase reporter viruses and replication-competent HIV-2 LTR mutants. Our results demonstrate that intact SpI binding sites are important for both HIV-2 and SIVmac LTR activity in T cells and monocyte-derived macrophages. In contrast, deletion of the NF-kB binding site or of upstream regulatory sequences impaired HIV-2 Rod LTR activity but had little effect on SIVmac239 promoter function. Thus, similar to HIV-1, regulation of HIV-2 LTR promoter activity shows a low degree of functional redundancy possibly suggesting a specific adaptation to the human host.

PU.1 binding to ets motifs within the equine infectious anemia virus long terminal repeat (LTR) enhancer: regulation of LTR activity and virus replication in macrophages

Binding of the transcription factor PU.1 to its DNA binding motif regulates the expression of a number of B-cell- and myeloid-specific genes. The long terminal repeat (LTR) of macrophage-tropic strains of equine infectious anemia virus (EIAV) contains three PU.1 binding sites, namely an invariant promoter-proximal site as well as two upstream sites. We have previously shown that these sites are important for EIAV LTR activity in primary macrophages (W. Maury, J. Virol. 68:6270-6279, 1994). Since the sequences present in these three binding motifs are not identical, we sought to determine the role of these three sites in EIAV LTR activity. While DNase I footprinting studies indicated that all three sites within the enhancer were bound by recombinant PU.1, reporter gene assays demonstrated that the middle motif was most important for basal levels of LTR activity in macrophages and that the 5' motif had little impact. The impact of the 3' site became evident in Tat transactivation studies, in which the loss of the site reduced Tat-transactivated expression 40-fold. In contrast, elimination of the 5' site had no effect on Tat-mediated activity. Binding studies were performed to determine whether differences in PU.1 binding affinity for the three sites correlated with the relative impact of each site on LTR transcription. While small differences were observed in the binding affinities of the three sites, with the promoter-proximal site having the strongest binding affinity, these differences could not account for the dramatic differences observed in the transcriptional effects. Instead, the promoter-proximal position of the 3' motif appeared to be critical for its transcriptional impact and suggested that the PU.1 sites may serve different roles depending upon the location of the sites within the enhancer. Infectivity studies demonstrated that an LTR containing an enhancer composed of the three PU.1 sites was not sufficient to drive viral replication in macrophages. These findings indicate that while the promoter-proximal PU.1 site is the most critical site for EIAV LTR activity in the presence of Tat, other elements within the enhancer are needed for EIAV replication in macrophages.

Exploiting hepatitis C virus activation of NFkappaB to deliver HCV-responsive expression of interferons alpha and gamma

Chronic infection with hepatitis C virus (HCV) may lead to liver failure and hepatocellular carcinoma. Current treatment for HCV includes high systemic doses of interferonalpha (IFNalpha), which is effective in less than half of patients and may have severe side effects. We designed conditional IFNalpha and IFNgamma expression constructs to be triggered by HCV-induced activation of NFkappaB, and delivered these using highly efficient recombinant Tag-deleted SV40-derived vectors. NFkappaB activates the HIV-1NL4-3 long terminal repeat (HIVLTR) as a promoter, which accounts for the conditional transgene expression. Human hepatocyte lines and primary rat hepatocytes (PRH) were transduced with SV[HIVLTR](IFN) vectors, and transfected with HCV cDNA. Production of human and murine IFNalpha and IFNgamma in cytosol and culture supernatants was measured. HCV activated the HIVLTR to produce and secrete IFNs, and did so largely through the NFkappaB binding sites of the HIVLTR. Levels of IFNs secreted, and the magnitude of induction in response to HCV, were greater in hepatocyte lines than in primary cultured hepatocytes. However, even in the latter, supernatant IFNalpha concentrations achieved by this approach were similar to therapeutic serum concentrations sought in systemic IFNalpha-treated patients. In coculture studies, secreted IFNalpha activated its cognate response elements in untransduced cells, suggesting that its potential inhibitory effects on HCV may not be limited to transduced cells. Although HCV replication in culture is difficult to assess, HCV-induced IFNalpha production demonstrably reduced HCV transcription. Conditional expression of IFNs within the liver may represent an attractive approach to therapy of severe chronic HCV infection that could avoid the side effects of systemic treatment regimens.

Mechanisms of constitutive NF-kappaB activation in human prostate cancer cells

BACKGROUND

Activation of the NF-kappaB transcription factor has been previously demonstrated in two androgen receptor negative prostate cancer cell lines. We wished to extend this work to additional prostate cancer cells and to characterize the mechanisms responsible for constitutive NF-kappaB activation.

METHODS

Electrophoretic mobility shift assays were performed to measure NF-kappaB DNA-binding activity in prostate cancer cell lines, and immunohistochemistry was performed to detect nuclear localization of NF-kappaB in prostate cancer tissues. Western blot analysis was used to study the status of IkappaBalpha. Transient transfection assays were employed to characterize the contributions of IkappaB kinase (IKK), MAPK kinase kinases (MAPKKKs), androgen receptor (AR), and tyrosine phosphorylation to the constitutive activation of NF-kappaB in the prostate cancer cell lines.

RESULTS

Constitutive NF-kappaB activity was observed in AR-negative cell lines as well as in the prostate cancer patient samples, but was not present in AR positive cells. A "super-repressor" IkappaBalpha, as well as dominant negative forms of IKKbeta and NF-kappaB-inducing kinase (NIK), and tyrosine kinase inhibition were able to suppress NF-kappaB activity in the cells with constitutive activation.

CONCLUSIONS

The constitutive activation of NF-kappaB observed in prostate cancer cells is likely due to a signal transduction pathway involving tyrosine kinases, NIK, and IKK activation.

The hepatitis B virus X protein induces HIV-1 replication and transcription in synergy with T-cell activation signals: functional roles of NF-kappaB/NF-AT and SP1-binding sites in the HIV-1 long terminal repeat promoter

Co-infection with hepatitis B virus (HBV) and human immunodeficiency virus type-1 (HIV-1) is relatively common. However, the impact of this co-infection on the clinical outcome of HIV infection has not been elucidated. We herein demonstrate that the HBV X protein (HBx) superinduces ongoing HIV-1 replication and HIV-1 long terminal repeat (LTR) transcription by synergizing with Tat protein and with T-cell activation signals. Although HBx cooperated with mitogenic stimuli in the induction of reporter plasmids harboring the HIV-1 kappaB enhancer, in both a NF-kappaB-dependent manner and a NF-AT-dependent manner, deletion of this element from the LTR did not affect the HBx-mediated up-regulation in the presence of Tat and/or mitogens. In contrast, mutation of the proximal LTR Sp1-binding sites abolished the HBx-mediated synergistic activation, but only when it was accompanied by deletion of the kappaB enhancer. When HBx was targeted to the nucleus, its ability to synergize with cellular activation stimuli was maintained. Furthermore, mutations of HBx affecting its interaction with the basal transcription machinery abrogated the synergistic activation by HBx, suggesting that this protein exerts its function by acting as a nuclear co-activator. These results indicate that HBx could contribute to a faster progression to AIDS in HBV-HIV co-infected individuals.

Regulation of equine infectious anemia virus expression

Equine infectious anemia virus (EIAV) is an ungulate lentivirus that is related to human immunodeficiency virus (HIV). Much of the understanding of lentiviral gene regulation comes from studies using HIV. HIV studies have provided insights into molecular regulation of EIAV expression; however, much of the regulation of EIAV expression stands in stark contrast to that of HIV. This review provides an overview of the current state of knowledge of EIAV regulation by comparing and contrasting EIAV gene regulation to HIV. The role of EIAV gene regulation is discussed in relation to EIAV pathogenesis.

Enhancement of the basal-level activity of HIV-1 long terminal repeat by HIV-1 nucleocapsid protein

Two HIV-1 proteins, Tat and NCp7 (NC), have zinc finger-like structures. NC is a virion protein and has been shown to accumulate in the nucleus 8 h postinfection. Since transcription factors with zinc fingers assist the transcriptional activity of both RNA polymerases II and III, we examined the effect of NC on HIV-1 LTR-directed gene expression. The HIV-1 NC binds to the HIV-1 LTR and results in a mobility shift in polyacrylamide gel electrophoresis. Competition assays with cold probes revealed that the binding of NC and formation of a DNA-protein complex could be prevented by the addition of excess unlabeled LTR self-probe, but not the HIV-1 V3 envelope gene. The DNase I footprint analysis showed that NC binds to six regions within HIV-1 LTR, four of which are near the transcription start site. The NC alone enhances LTR basal-level activity in RNA runoff experiments. When the general transcription factors (GTFs) were added in the assay, NC enhances NF-kappaB, Sp1, and TFIIB-induced HIV-1 LTR-directed RNA transcription. RNA transcription directed by the adenovirus major late promoter, however, is not significantly affected by NC in the cell-free system. Transient transfection of human T lymphocytes with the plasmids containing HIV-1 nc or gag showed enhancement of LTR-CAT activity. Moreover, transfection of HIV-1 provirus containing mutations in NC zinc-finger domains dramatically decreases the enhancement activity in human T cells, in which HIV-1 LTR is stably integrated into the cellular genome. These observations show that NC binds to HIV-1 LTR and cooperatively enhances GTFs and NF-kappaB induced HIV-1 LTR basal-level activity. NC may play the role of a nucleation protein, which binds to LTR and enhances basal-level transcription by recruiting cellular transcription factors to the HIV-1 promoter in competition with cellular promoters.

Green fluorescence protein as a transcriptional reporter for the long terminal repeats of the human immunodeficiency virus type 1

Using the enhanced green fluorescence protein (EGFP), a transient reporter expression system was established to assess the transcriptional activity of the long terminal repeats (LTR) of primary isolates of the human immunodeficiency virus type 1 (HIV-1). Consistent with the conventional chloramphenicol acetyl transferase (CAT) reporter, EGFP expression, under the direction of HIV-1 LTR, was readily detected in the transient transfection and was elevated by co-transfection of HIV-1 tat-expression vector. Comparing to CAT, however, EGFP expression system has two advantages: (i) Using a fluorescence activated cell sorter (FACS), it was possible to simultaneously measure transfection efficiency and fluorescence intensity of the transfected live cells without the necessity of co-transfection of a reference plasmid for comparing the transcriptional activity of two promoters; and (ii) EGFP expression was readily detected at a DNA concentration where CAT activity was not detectable possibly because the transfectants could be 'gated'. On the other hand, at a higher concentration of DNA, CAT signal became more prominent than that of EGFP, possibly because the enzymatic activity of CAT 'amplified' the signal. EGFP fluorescence detected by FACS was a direct measurement of the expressed chromophore. It is concluded that the system is rapid, reproducible, convenient and useful for quantitative analysis of transcription.

The nuclear receptor chicken ovalbumin upstream promoter transcription factor interacts with HIV-1 Tat and stimulates viral replication in human microglial cells

Human immunodeficiency virus type 1 (HIV-1) infects the central nervous system and plays a direct role in the pathogenesis of AIDS dementia. However, the molecular mechanisms underlying HIV-1 expression in the central nervous system are poorly understood. We have recently reported that the nuclear receptor chicken ovalbumin upstream promoter transcription factor (COUP-TF), an orphan member of the nuclear receptor superfamily, is an activator of HIV-1 gene transcription. Here, our results show that COUP-TF stimulates HIV-1 transcription in primary cultured human microglial cells, the primary target for HIV-1 infection in brain. Run-on assays indicated that COUP-TF acts on the initiation step of transcription. Results from reverse transcription-polymerase chain reaction and immunocytochemistry analysis further revealed the importance of this factor by demonstrating that overexpression of COUP-TF leads to initiation of viral replication in primary HIV-infected human microglia. In addition, COUP-TF is able to physically interact and cooperate with the viral transactivator Tat. The combination of COUP-TF and Tat leads to NF-kappaB- and Sp1-independent enhanced transcriptional stimulation. In vitro binding studies showed that COUP-TF interacts with Tat through amino acids within the N-terminal DNA-binding domain of COUP-TF. Amino acids 48-72 in the basic and C-terminal regions of Tat are required for the binding of Tat to COUP-TF. These results suggest that COUP-TF is an essential transcription factor involved in HIV-1 expression in microglia and reveal a novel interplay of Tat and COUP-TF during regulation of viral expression.

ZFX transactivation of the HIV-1 LTR is cell specific and depends on core enhancer and TATA box sequences

The ZFX gene is ubiquitously transcribed and highly conserved among vertebrates. The integrity of Zfx, its murine homologue, has been shown to be important for growth during embryogenesis and sustained gamete production. Alternative splicing was shown to result in production of mRNAs coding for either ZFX804or a shorter isoform initiated downstream, ZFX575. ZFX575was previously shown to be a potent transactivator of the HLA-A11 promoter. Here, the HIV-1 LTR is also shown to be potently transactivated by ZFX575in several cell types, while ZFX804activity is found to be similar to that of ZFX575, null or intermediary according to the cell type. In all cell types, the HIV-1 TATA box sequence is a key element of transactivation, while the Sp1 or NFkappaB sites are variably required, according to the cell type. Overall, the results suggest that ZFX575and ZFX804could play a role in HIV-1 LTR induction as co-activators enhancing productive interactions between upstream transactivators and the basal transcription complexes recruited by the TATA box.

Genetic instability of live, attenuated human immunodeficiency virus type 1 vaccine strains

Live, attenuated viruses have been the most successful vaccines in monkey models of human immunodeficiency virus type 1 (HIV-1) infection. However, there are several safety concerns about using such an anti-HIV vaccine in humans, including reversion of the vaccine strain to virulence and recombination with endogenous retroviral sequences to produce new infectious and potentially pathogenic viruses. Because testing in humans would inevitably carry a substantial risk, we set out to test the genetic stability of multiply deleted HIV constructs in perpetuated tissue culture infections. The Delta3 candidate vaccine strain of HIV-1 contains deletions in the viral long terminal repeat (LTR) promoter and the vpr and nef genes. This virus replicates with delayed kinetics, but a profound enhancement of virus replication was observed after approximately 2 months of culturing. Analysis of the revertant viral genome indicated that the three introduced deletions were maintained but a 39-nucleotide sequence was inserted in the LTR promoter region. This insert was formed by duplication of the region encoding three binding sites for the Sp1 transcription factor. The duplicated Sp1 region was demonstrated to increase the LTR promoter activity, and a concomitant increase in the virus replication rate was measured. In fact, duplication of the Sp1 sites increased the fitness of the Delta3 virus (Vpr/Nef/U3) to levels higher than that of the singly deleted DeltaVpr virus. These results indicate that deleted HIV-1 vaccine strains can evolve into fast-replicating variants by multiplication of remaining sequence motifs, and their safety is therefore not guaranteed. This insight may guide future efforts to develop more stable anti-HIV vaccines.

Nuclear levels of NF-kappaB correlate with syncytium-forming capacity of 8e51 cells, expressing a defective HIV virus

The double NF-kappaB site identified in the LTR of the human immunodeficiency virus-1 (HIV-1) has been demonstrated to be necessary for efficient viral transcription. In this report we present the characterisation of NF-kappaB subunits engaged in complexes binding to the HIV-1 NF-kappaB site in human 8e51 T-cells, that harbour a defective HIV-1. At least four different specific NF-kappaB complexes are present in the nucleus of these cells. With the use of specific antibodies we have determined the composition of each complex using electrophoretic mobility shift assays. The results show the presence of several NF-kappaB family members, with the transactivating RelA being engaged in multiple complexes. The importance of NF-kappaB complexes in viral functions has been established comparing the level of NF-kappaB DNA-binding complexes with syncytia-forming activity of 8e51 cells. In fact, 8e51 cells that had almost lost their syncytia-forming capacity were found to contain at least 10 times less active NF-kappaB DNA-binding complex than the actively fusing cells. The correlation is specific as the level of at least three other transcription factors did not change.

Genotypic and phenotypic characterization of long terminal repeat sequences from long-term survivors of human immunodeficiency virus type 1 infection

Human immunodeficiency virus type 1 (HIV-1)-infected individuals who remain asymptomatic despite prolonged infection present a unique opportunity to understand virologic and immunologic factors involved in the pathogenesis of AIDS. We have previously identified a group of long-term survivors (LTS) who are clinically healthy and immunologically normal despite 13 to 15 years of HIV-1 infection. In this study, we examined the 5' long terminal repeat (5' LTR) sequences in eight of these LTS. A total of 29 nucleotide sequences were obtained from their peripheral blood mononuclear cells (PBMC). Analysis of these sequences revealed no gross deletions within the 5' LTR. Seven of the eight subjects shared nearly identical consensus sequences in the binding sites for NF-kappaB, Sp1, and the viral trans-activator Tat. In multiple samples from one individual (Pt 5), however, G-to-A hypermutations were found throughout the entire region, suggesting a genetically defective 5' LTR. The effects of the observed genetic variations on LTR transcription were studied by transient transfection of an LTR-driven luciferase reporter gene and by infection with a full-length recombinant HIV-1 containing a luciferase reporter (HIVHXBLTRluc). A wide range of basal and Tat-induced transcriptional activities was found among the 5' LTR from seven of the eight LTS in both transfected 293 cells and donor PBMC, suggesting a functionally intact 5' LTR in these individuals. It is therefore unlikely that defects in the 5' LTR are the underlying explanation for the benign clinical course associated with these seven individuals. However, functional abnormalities were found in the LTR from Pt 5 in directing both heterologous and viral gene expression, providing a possible genetic explanation for the low viral load and prolonged asymptomatic state of this individual. Last, a similar overall degree of genetic diversity was found among viruses from the LTS compared to those from patients with AIDS, reinforcing the notion that a strong correlation between the degree of genetic diversity and the rate of disease progression is unlikely.

Simian immunodeficiency viruses containing mutations in the long terminal repeat NF-kappa B or Sp1 binding sites replicate efficiently in T cells and PHA-stimulated PBMCs

The long terminal repeats (LTRs) of primate lentiviruses contain conserved binding sites for the NF-kappa B and Sp1 cellular transcription factors. In order to study the role that these sites play in simian immunodeficiency virus (SIV) replication, we have introduced mutations that disrupt either the NF-kappa B or Sp1 binding sites in the LTR of an infectious molecular clone of SIVmac239. An additional mutation also disrupted the SF3 transcription factor binding site that overlaps the NF-kappa B site. Viruses containing point mutations or deletions of the NF-kappa B, SF3, or Sp1 binding sites retained the ability to replicate efficiently in the CEMx174 and MT4 cell lines, as well as in PHA-stimulated primary rhesus macaque peripheral blood mononuclear cells (PBMCs). Efficient replication of SIVs mutated in either NF-kappa B or Sp1 binding sites suggests that the SIV LTR promoter contains multiple functionally redundant elements capable of supporting sufficient transcription to allow productive viral replication.

Enhancement or inhibition of HIV-1 replication by intracellular expression of sense or antisense RNA targeted at different intermediates of reverse transcription

OBJECTIVES

To construct retroviral vectors expressing sense or antisense RNA targeted at HIV reverse transcription intermediates, and to test the anti-HIV properties of these constructs in transduced T cells.

DESIGN

Five double-copy retroviral vectors were constructed, in which the expression of the sense or antisense RNA corresponding to HIV minus- or plus-strand strong-stop DNA was driven by the human tRNA(met) promoter.

METHOD

The templates for the sense or antisense RNA were polymerase chain reaction-cloned from HIV pNL43 into a murine leukaemia virus-based vector and corresponding defective virions were packaged in PA317 cells. Human Jurkat T cells transduced with these vectors were challenged with HIV and monitored for viral RNA, viral DNA and p24 production for 23 weeks.

RESULTS

Intracellular expression of HIV sense RU5 sequences (RNA complementary to minus-strand strong-stop DNA) enhanced HIV replication in T cells. Expression of HIV sense or antisense U3RU5 sequences (identical or complementary to plus-strand strong-stop DNA) conferred long-term inhibition of HIV replication, despite continuous presence of viral challenge in the transduced cell cultures.

CONCLUSION

Plus-strand strong-stop DNA as an intermediate in the early process of viral reverse transcription can be explored as an additional target for anti-HIV gene therapy.

TAR and Sp1-independent transactivation of HIV long terminal repeat by the Tat protein in the presence of human cytomegalovirus IE1/IE2

OBJECTIVE

The HIV Tat protein is a transcriptional transactivator of the HIV-1 long terminal repeat (LTR) promoter element. Its activity depends on its direct interaction with the trans-activation response (TAR) element, although TAR-independent activation by Tat has been demonstrated in different cells. Herpesviruses in general and human cytomegalovirus (HCMV) in particular are often isolated from HIV-1-infected patients and could play a role in the activation of latent HIV and in a subsequent increase in HIV replication. HCMV immediate early gene products (IE1 and IE2) are nuclear phosphoproteins that play a pivotal role in HCMV replication and have been shown to transregulate both viral and cellular gene expression. It has repeatedly been shown that HCMV IE1/IE2 can independently transactivate HIV-1 LTR. The aim of this study was to investigate IE1/IE2 transactivation of HIV-1 LTR in a CD4+ T-cell line in the absence and presence of HIV-1 Tat to establish whether IE1/IE2 can synergize with Tat.

METHODS

HIV-1 LTR transactivation by HCMV IE1/IE2 in the presence and absence of HIV-1 Tat was determined by transient transfection experiments of J-Jhan lymphoblastoid cells with a series of different expression vectors.

RESULTS

We found a strong synergistic transactivation between HIV Tat and the IE1-IE2 complex on HIV LTR activity using vectors driven either by wild-type LTR or by the nuclear factor NF-kappa(B) response element-mutated HIV LTR. IE1/IE2 synergism with HIV Tat was also observed in Sp1 binding site-mutated for TAR-deleted LTR, which cannot be activated by Tat alone. This cooperation is abolished when the region in IE2 that binds the TATA box binding protein is deleted.

CONCLUSIONS

The results obtained indicate that Sp1-binding and TAR sequences are not strictly required for Tat responsiveness when Tat is directed to the HIV promoter by HCMV IE1-IE2. This synergistic effect is mediated by the IE2 and TATA-binding region, and could play a major role in HIV activation when cells are infected by both viruses, a feature often observed in AIDS patients.

Induction of AIDS by simian immunodeficiency virus lacking NF-kappaB and SP1 binding elements

Rhesus monkeys (Macaca mulatta) were infected with five strains of simian immunodeficiency virus (SIV) derived from SIVmac239 containing deletions (delta) or substitutions (subst) in NF-kappaB and Sp1 binding sites. We have shown previously that mutations in these regions still allow efficient SIVmac replication in primary lymphoid cell cultures (P. O. Ilyinskii and R. C. Desrosiers, J. Virol. 70:3118-3126, 1996). Two animals were inoculated intravenously with each mutant strain of SIVmac239: delta NFkappaB, delta Sp1234, delta NFkappaB delta Sp1234, substSp12, and substSp1234. All but one of the infected animals showed an early spike in plasma antigenemia, maintained high virus burdens, and had significant changes in lymphoid tissues, and six died with AIDS within the first 60 weeks of infection. One of the animals infected with the SIV strain delta NFkappaB delta Sp1234 showed lower levels of plasma antigenemia and lower virus burdens; the other animal infected with this same mutant strain died with AIDS 17 weeks after inoculation. No consistent novel mutations or reversions were detected in proviral sequences derived from the animals infected with the deletion mutants and the substSp12 mutant by 20 weeks postinfection. Point-mutated sequences were partially deleted in both animals infected with the substSp1234 strain. These results indicate that the NF-kappaB and Sp1 binding sites are not essential for the induction of AIDS by SIVmac239. They also provide indirect evidence for the importance of a novel enhancer element in the U3 region of the SIVmac long terminal repeat that is located immediately upstream of the NF-kappaB binding site within the C-terminal region of the nef coding sequence.

Identification of a replication-competent pathogenic human immunodeficiency virus type 1 with a duplication in the TCF-1alpha region but lacking NF-kappaB binding sites

Multiple human immunodeficiency virus type 1 (HIV-1) sequences with deletions of NF-kappaB binding sites at both the 5' and 3' long terminal repeats (LTRs) were identified in serial samples collected from an infected individual. The effect of this deletion on the level of transcription was studied by transient transfection of an LTR-driven luciferase reporter gene and by infection with a full-length recombinant HIV-1 containing a luciferase reporter (HIVHXBluc). Detectable levels of gene expression were found in both systems, in the presence or absence of the viral transactivator Tat. Interestingly, a duplication of a putative TCF-1alpha motif was found in place of the NF-kappaB elements in these viruses. Higher transcriptional activity was observed with HXBLTR (NF-kappaB intact) than with the patient's LTR (NF-kappaB deleted), suggesting that the NF-kappaB binding sites may promote optimal levels of viral gene transcription. The ability of these viruses with NF-kappaB deleted to replicate and cause substantial decline in CD4 cell counts demonstrates that the NF-kappaB binding sites are not absolutely required for viral replication or pathogenicity in vivo. These results are consistent with the notion that the HIV-1 LTR possesses functional redundancy which allows it to interact with multiple transcription factors, thereby ensuring viral replication in a variety of cell types.

A gene for a novel zinc-finger protein expressed in differentiated epithelial cells and transiently in certain mesenchymal cells

We have identified a novel zinc-finger protein whose mRNA is expressed at high levels in the epidermal layer of the skin and in epithelial cells in the tongue, palate, esophagus, stomach, and colon of newborn mice. Expression in epithelial cells is first detected at the time of their differentiation during embryonic development. In addition, during early embryonic development there is expression in mesenchymal cells of the skeletal primordia and the metanephric kidney which is later down-regulated. The expression pattern suggests that the protein could be involved in terminal differentiation of several epithelial cell types and could also be involved in early differentiation of the skeleton and kidney. The carboxyl terminus of the protein contains three zinc fingers with a high degree of homology to erythroid krüppel-like factor and binds to DNA fragments containing CACCC motifs. The amino-terminal portion of the protein is proline and serine-rich and can function as a transcriptional activator. The chromosomal location of the gene was mapped using mouse interspecific backcrosses and was shown to localize to mouse chromosome 4 and to cosegregate with the thioredoxin gene.

An NF-kappaB site in the 5'-untranslated leader region of the human immunodeficiency virus type 1 enhances the viral expression in response to NF-kappaB-activating stimuli

The 5'-untranslated leader region of human immunodeficiency virus, type 1 (HIV-1), includes a complex array of putative regulatory elements whose role in the viral expression is not completely understood. Here we demonstrate the presence of an NF-kappaB-responsive element in the trans-activation response (TAR) region of HIV-1 that confers the full induction of HIV-1 long terminal repeat (LTR) in response to NF-kappaB-activating stimuli, such as DNA alkylating agents, phorbol 12-myristate 13-acetate, and tumor necrosis factor-alpha. The TAR NF-kappaB site GGGAGCTCTC spans from positions +31 to +40 and cooperates with the NF-kappaB enhancer upstream of the TATA box in the NF-kappaB-mediated induction of HIV-1 LTR. The conclusion stems from the following observations: (i) deletion of the two NF-kappaB sites upstream of the TATA box reduces, but does not abolish, the HIV-1 LTR activation by NF-kappaB inducers; (ii) deletion or base pair substitutions of the TAR NF-kappaB site significantly reduce the HIV-1 LTR activation by NF-kappaB inducers; (iii) deletions of both the NF-kappaB sites upstream of the TATA box and the TAR NF-kappaB site abolish the activation of HIV-1 LTR in response to NF-kappaB inducers. Moreover, the p50 p65 NF-kappaB complex binds to the TAR NF-kappaB sequence and trans-activates the TAR NF-kappaB-directed expression. The identification of an additional NF-kappaB site in the HIV-1 LTR points to the relevance of NF-kappaB factors in the HIV-1 life cycle.

C/EBP activators are required for HIV-1 replication and proviral induction in monocytic cell lines

Previous work has shown that C/EBP sites and C/EBP transcriptional activators are necessary for HIV-1 LTR activity in monocytes/macrophages. We have investigated the role that C/EBP proteins play in induction and replication of HIV-1. Ectopic expression of the dominant negative C/EBP protein LIP inhibited HIV-1 mRNA and virus production in activated U1 cells, demonstrating that C/EBP proteins are required for provirus induction. U1 lines overexpressing C/EBP activator NF-IL-6 produced more viral mRNA and virus particles following cellular activation than control lines, demonstrating that C/EBP proteins are limiting for virus transcription. HIV-1 harboring mutations within two C/EBP sites were crippled in their ability to replicate in U937 promonocytic cells, indicating that these sites are required for replication. These data identify C/EBP proteins as regulators of HIV-1 expression in monocytes/macrophages.

Efficient transcription and replication of simian immunodeficiency virus in the absence of NF-kappaB and Sp1 binding elements

Ten mutants of the simian immunodeficiency virus (SIV) SIVmac239 bearing deletions (delta) or substitutions (subst) in the NF-kappaB and/or Sp1 binding elements were created, and the replicative capacities of the mutants were analyzed. All mutants, including one extensively mutagenized strain entirely missing the NF-kappaB and four Spl binding elements, replicated with wild-type kinetics and to a wild-type level in peripheral blood mononuclear cell cultures in 50 to 100% of the experiments. One group of mutants replicated very similarly to SIVmac239 in kinetics and yield in CEMxl74 cells (2xNFKappaB > or = SlVmac239 approximately deltaNFkappaB approximately deltaSpl234 approximately substNFkappaB approximately substSpl2 approximately substSp23), while a second group replicated with delayed or slightly delayed kinetics in CEMxl74 cells (SIVmac239 > substSp34 > deltaNFkappaBdeltaSpl234 approximately deltaNFkappaBdeltaSp1 > substSpl234). Reversions or additional mutations were not detected in the U3 and R regions of proviral DNA from CEMxl74 cells infected with the SIVmac239 mutants. Similar results were obtained when mutants of SIVmacMER (a macrophage-competent derivative of SIVmac239) were tested in peripheral blood mononuclear cell and CEMx174 cultures. However, the growth of most mutated viruses was suppressed in primary rhesus monkey alveolar macrophages (SIVmacMER approximately 2xNFkappaB approximately substNFkappaB > deltaNFkappaB > deltaNFkappaBdeltaSpl234 approximately deltaNFkappaBdeltaSpl > deltaSpl234 approximately substSpl2 > substSp23 approximately substSp34 approximately substSpl234 > or = SIVmac239). Thus, changes in the Sp1 binding sites had the most dramatic effects on SIVmac replication in primary macrophage cultures. Analysis of long terminal repeat-driven secreted alkaline phosphatase activity in transient assays showed that, unlike human immunodeficiency virus type 1, the SIV long terminal repeat possesses an enhancer region just upstream of the NF-kappaB element which maintains significant levels of basal transcription in the absence of NF-kappaB and Sp1 sites. This region is responsive to transactivation by Tat. In addition, the SIV TATA box was shown to be stronger than that of human immunodeficiency virus type 1. Therefore, the surprisingly high replicative capacity of NF-kappaB and Sp1 binding site mutants of SIVmac is due to unique features or the enhancer/promoter region.

Protein kinase C-zeta mediates NF-kappa B activation in human immunodeficiency virus-infected monocytes

The molecular mechanisms regulating human immunodeficiency virus (HIV) persistence in a major cell reservoir such as the macrophage remain unknown. NF-kappa B is a transcription factor involved in the regulation of the HIV long terminal repeat and is selectively activated following HIV infection of human macrophages. Although little information as to what signal transduction pathways mediate NF-kappa B activation in monocytes-macrophages is available, our previous work indicated that classical protein kinase C (PKC) isoenzymes were not involved in the HIV-mediated NF-kappa B activation. In this study, we have focused on atypical PKC isoenzymes. PKC-zeta belongs to this family and is known to be an important step in NF-kappa B activation in other cell systems. Immunoblotting experiments with U937 cells demonstrate that PKC-zeta is present in these cells, and its expression can be downmodulated by antisense oligonucleotides (AO). The HIV-mediated NF-kappa B activation is selectively reduced by AO to PKC-zeta. In addition, cotransfection of a negative dominant molecule of PKC-zeta (PKC-zeta mut) with NF-kappa B-dependent reporter genes selectively inhibits the HIV- but not phorbol myristate acetate- or lipopolysaccharide-mediated activation of NF-kappa B. That PKC-zeta is specific in regulating NF-kappa B is concluded from the inability of PKC-zeta(mut) to interfere with the basal or phorbol myristate acetate-inducible CREB- or AP1-dependent transcriptional activity. Lastly, we demonstrate a selective inhibition of p24 production by HIV-infected human macrophages when treated with AO to PKC-zeta. Altogether, these results suggest that atypical PKC isoenzymes, including PKC-zeta, participate in the signal transduction pathways by which HIV infection results in the activation of NF-kappa B in human monocytic cells and macrophages.

Selective infection of human T-lymphotropic virus type 1 (HTLV-1)-infected cells by chimeric human immunodeficiency viruses containing HTLV-1 tax response elements in the long terminal repeat

Previous studies have suggested that the human immunodeficiency virus long terminal repeat (HIV LTR) enhancer/promoter sequences contribute to the replication ability of HIV in different T-cell lines; mutation of these sequences can alter HIV tropism. We have utilized site-specific mutagenesis to generate variants of HIV that exhibit specific tropism for human T-lymphotropic virus type 1 (HTLV-1) Tax-expressing CD4+ T cells. The wild-type HIV LTR NF-kappa B and Sp1 sites in an infectious molecular clone of HIV type 1 were replaced with sequences derived from the 21-bp Tax response elements (TRE) from the HTLV-1 LTR to generate TRE-containing chimeric HIVs (TRE-HIVs). The TRE-HIVs exhibit selective replication and cell killing in HTLV-infected human CD4+ T cells, but not in HTLV-negative T cells. Transient transfections suggested that Tax-TRE interactions could account for the observed replication specificity. The TRE-containing HIV LTRs were synergistically activated by the HIV Tat and HTLV-1 Tax transactivators. These results demonstrate that it is possible to specifically target HIV replication and cytotoxicity to HTLV-1+, CD4+ human T cells, on the basis of Tax-TRE interactions, and provide a model for the development of specific, cytotoxic, retroviral gene therapy vectors for HTLV-1-infected cells based on alterations of the LTR transcriptional regulatory elements. They also suggest that HIV Tat can cooperate with heterologous transcriptional activators, such as Tax, which act through upstream binding sites without directly binding to DNA.

Regulation of human immunodeficiency virus type 1 and cytokine gene expression in myeloid cells by NF-kappa B/Rel transcription factors

CD4+ macrophages in tissues such as lung, skin, and lymph nodes, promyelocytic cells in bone marrow, and peripheral blood monocytes serve as important targets and reservoirs for human immunodeficiency virus type 1 (HIV-1) replication. HIV-1-infected myeloid cells are often diminished in their ability to participate in chemotaxis, phagocytosis, and intracellular killing. HIV-1 infection of myeloid cells can lead to the expression of surface receptors associated with cellular activation and/or differentiation that increase the responsiveness of these cells to cytokines secreted by neighboring cells as well as to bacteria or other pathogens. Enhancement of HIV-1 replication is related in part to increased DNA-binding activity of cellular transcription factors such as NF-kappa B. NF-kappa B binds to the HIV-1 enhancer region of the long terminal repeat and contributes to the inducibility of HIV-1 gene expression in response to multiple activating agents. Phosphorylation and degradation of the cytoplasmic inhibitor I kappa B alpha are crucial regulatory events in the activation of NF-kappa B DNA-binding activity. Both N- and C-terminal residues of I kappa B alpha are required for inducer-mediated degradation. Chronic HIV-1 infection of myeloid cells leads to constitutive NF-kappa B DNA-binding activity and provides an intranuclear environment capable of perpetuating HIV-1 replication. Increased intracellular stores of latent NF-kappa B may also result in rapid inducibility of NF-kappa B-dependent cytokine gene expression. In response to secondary pathogenic infections or antigenic challenge, cytokine gene expression is rapidly induced, enhanced, and sustained over prolonged periods in HIV-1-infected myeloid cells compared with uninfected cells. Elevated levels of several inflammatory cytokines have been detected in the sera of HIV-1-infected individuals. Secretion of myeloid cell-derived cytokines may both increase virus production and contribute to AIDS-associated disorders.

A proliferative p53-responsive element mediates tumor necrosis factor alpha induction of the human immunodeficiency virus type 1 long terminal repeat

Transforming mutants of the p53 tumor suppressor gene can positively regulate transcription from several promoters that do not contain known p53 binding sites. Here, we report the identification of a novel p53 binding site in the human immunodeficiency virus long terminal repeat that specifically mediates mutant p53 transactivation. This DNA element was bound by endogenous Jurkat p53 when these cells were stimulated by tumor necrosis factor. Mutation of this sequence inhibited p53 transactivation and tumor necrosis factor inducibility of the human immunodeficiency virus type 1 long terminal repeat. In addition, this DNA element was found to be sufficient to confer mutant p53 responsiveness on a heterologous minimal promoter. It has been hypothesized that transforming mutants of p53 represent a proliferative conformational stage that can be adopted by the native protein under stimulation by growth factors. The data presented suggest that proliferative and antiproliferative p53 conformations recognize different DNA binding sites in order to mediate distinct biological functions. Thus, transforming mutants of p53 that fold into the proliferative conformation would favor proliferative over antiproliferative functions.

Tat-independent replication of human immunodeficiency viruses

The replication of human immunodeficiency retroviruses involves a complex series of events that is regulated at both transcriptional and posttranscriptional levels. The tat gene product is a potent trans-activator of viral transcription and therefore an attractive target for the development of antiviral drugs. Tat-defective HIV-1 proviral DNA clones have been shown previously to be replication defective. In this study, we report that tat-defective HIV-1 and HIV-2 viral DNA transfected into U937 cells can direct efficient viral replication in the presence of transcriptional stimulators such as TNF-alpha and PMA. In MT-4 cells, tat-defective HIV-1 can replicate without any stimulation. The viruses recovered from MT-4 cells remained tat defective defined by their inability to infect T cell lines (e.g., Molt 4/8) although replication could be rescued with cytokines. Limited replication was observed in primary mononuclear cells. Furthermore, we showed that Ro 24-7429, a potent tat antagonist and antiviral compound, failed to suppress HIV-1 replication in TNF-alpha-stimulated T cells. These results have important implications for targeting tat as a therapeutic strategy for AIDS.

An interaction between the DNA-binding domains of RelA(p65) and Sp1 mediates human immunodeficiency virus gene activation

Induction of human immunodeficiency virus type 1 (HIV-1) gene expression in stimulated T cells has been attributed to the activation of the transcription factor NF-kappa B. The twice-repeated kappa B sites within the HIV-1 long terminal repeat are in close proximity to three binding sites for Sp1. We have previously shown that a cooperative interaction of NF-kappa B with Sp1 is required for the efficient stimulation of HIV-1 transcription. In this report, we define the domains of each protein responsible for this effect. Although the transactivation domains seemed likely to mediate this interaction, we find, surprisingly, that this interaction occurs through the putative DNA-binding domains of both proteins. Sp1 specifically interacted with the amino-terminal region of RelA(p65). Similarly, RelA bound directly to the zinc finger region of Sp1. This interaction was specific and resulted in cooperative DNA binding to the kappa B and Sp1 sites in the HIV-1 long terminal repeat. Furthermore, the amino-terminal region of RelA did not associate with several other transcription factors, including MyoD, E12, or Kox15, another zinc finger protein. These findings suggest that the juxtaposition of DNA-binding sites promotes a specific protein interaction between the DNA-binding regions of these transcription factors. This interaction is required for HIV transcriptional activation and may provide a mechanism to allow for selective activation of kappa B-regulated genes.

Transcription factor AP-2 regulates human immunodeficiency virus type 1 gene expression

Human immunodeficiency virus type 1 (HIV-1) gene expression is regulated by an enhancer region composed of multiple potential cis-acting regulatory sites. Here, we describe binding sites for the transcription factor AP-2 in the HIV-1 long terminal repeat which modulate HIV enhancer function. One site is embedded within the two previously described kappa B elements, and a second site is detected further downstream. DNase I footprinting and electrophoretic mobility shift assay experiments demonstrated that AP-2 binds to the site between the kappa B elements. Interestingly, AP-2 and NF-kappa B bind to this region in a mutually exclusive manner. Mutations which disrupt this AP-2-binding site lower basal levels of transcription but do not affect NF-kappa B-mediated induction by tumor necrosis factor alpha in Jurkat T leukemia cells.

An interaction between the DNA-binding domains of RelA(p65) and Sp1 mediates human immunodeficiency virus gene activation

Induction of human immunodeficiency virus type 1 (HIV-1) gene expression in stimulated T cells has been attributed to the activation of the transcription factor NF-kappa B. The twice-repeated kappa B sites within the HIV-1 long terminal repeat are in close proximity to three binding sites for Sp1. We have previously shown that a cooperative interaction of NF-kappa B with Sp1 is required for the efficient stimulation of HIV-1 transcription. In this report, we define the domains of each protein responsible for this effect. Although the transactivation domains seemed likely to mediate this interaction, we find, surprisingly, that this interaction occurs through the putative DNA-binding domains of both proteins. Sp1 specifically interacted with the amino-terminal region of RelA(p65). Similarly, RelA bound directly to the zinc finger region of Sp1. This interaction was specific and resulted in cooperative DNA binding to the kappa B and Sp1 sites in the HIV-1 long terminal repeat. Furthermore, the amino-terminal region of RelA did not associate with several other transcription factors, including MyoD, E12, or Kox15, another zinc finger protein. These findings suggest that the juxtaposition of DNA-binding sites promotes a specific protein interaction between the DNA-binding regions of these transcription factors. This interaction is required for HIV transcriptional activation and may provide a mechanism to allow for selective activation of kappa B-regulated genes.